Approximately 62 million people in this world are estimated to have some form of paralysis, and approximately 10 million people are estimated to have received an amputation. One of the techniques utilized to afford greater mobility to amputees is myoelectric prosthesis. Myoelectric prosthesis typically involves the measurement of electrical activity in a contracting muscle located close to the site of the paralysis/amputation and using the measurement to provide suitable electrical stimuli to the paralyzed muscle or to residual functioning muscle. In essence, myoelectric prosthesis enables individuals to control a paralyzed muscle (or robotic prosthetics) through a residual functioning muscle. Unfortunately, the degree of motor function returned via myoelectric prosthesis is limited, largely due to the prosthetic's inability to extract sufficient information from a working muscle or to adequately control paralyzed muscle via electrical stimulation. Furthermore, existing devices and techniques used for performing myoelectric prosthesis suffer from various limitations.
To elaborate upon a first limitation, attention is drawn to a first prior art reference document titled “Microelectrodes with Three-dimensional Structures for Improved Neural Interfacing,” by S. Metz et al, and further to a second prior art reference document titled “A Three-Dimensional Multi-electrode Array for Multi-site Stimulation and Recording in Acute Brain Slices,” by Marc Olive Heuschkel et. al.
The teachings in these two prior art reference documents may be summarized using FIG. 1 that is shown herein in this disclosure.
Prior art microelectrode device 110, which is coupled to an electrical stimulus transmitter/response signal receiver 105, contains a number of microelectrodes that are mounted on a rigid glass substrate and are shaped for penetrating a tissue slice 115. More particularly, the microelectrodes are pyramid-shaped microelectrodes that are allegedly advantageous for penetrating dead cell layer 116 and getting closer to active cells located below dead cell layer 116.
While microelectrode device 110 does provide certain advantages for in-vitro applications, the rigid nature of the glass substrate and the size of the device (for example, a 60 microelectrode device is shown to have a size of 5×5 cm2) make this prior art device unsuitable for many in-vivo applications, especially when it is desired to implant such a device upon a small-sized live organ, live muscle or live tissue.
This aspect is illustrated in FIG. 2. When microelectrode device 110 is implanted upon organ 125, which may be an internal organ of a rat for example, the rigid nature of the substrate and the size of the device 110 permit only a few of the microelectrodes from penetrating the outer layer of organ 125. Furthermore, it can be understood that the projecting portion of device 110 may make undesirable contact with adjacent organs (not shown) and may potentially cause damage to these adjacent organs.
The disadvantages described above with reference to prior art microelectrode device 110 are alleviated to some extent by a different prior art microelectrode device 130 that is disclosed in a third prior art reference document titled “PDMS-Based Stretchable Multi-Electrode and Chemotrode Array for Epidural and Subdural Neuronal Recording, Electrical Stimulation and Drug Delivery” (International Publication Number WO 2011/157714 A1).
As shown in FIG. 3, device 130 not only incorporates a flexible substrate that conforms to a surface layer of organ 125, but also includes certain features that are allegedly advantageous for in-vivo applications wherein placement of the microelectrodes to the proximity of an organ, such as the spinal cord of a rat, is desirable. As described in the third prior art reference document, the non-penetrating nature of the microelectrodes makes the implantation less invasive and less traumatic—thereby teaching away from the use of penetrating microelectrodes such as those disclosed in the first and second prior art reference documents.
More particularly, device 130 is placed such that surrounding tissue material (dura matter for example) located above and below device 130, provides an anchoring action to keep device 130 in place without damaging the spinal cord. The lack of an intrinsic anchoring element in device 130 makes it difficult or impossible to use device 130 upon certain tissue surfaces where surrounding tissue or other structures are unavailable to hold device 130 in place.
Furthermore, the size and shape of the spinal cord necessitates that device 130 have a relatively large and elongated shape (together with relatively large dimensions for pads, tracks, holes etc.). In this context, it may be pertinent to draw attention to FIGS. 11 and 12 of the third prior art reference document and the associated description, which discloses a conductive track width of 150 μm, minimum distance between adjacent tracks if 150 μm, diameter of each microelectrode is 350 μm, and holes of 350 μm diameter. While such dimensions may be acceptable for mounting on to relatively large organs, these dimensions are not suitable for use when the organ is very small in size.
In view of the above-mentioned remarks, it would be desirable to make certain improvements to existing microelectrode devices.